The invention relates generally to servo-controlled systems, and more particularly to reducing acoustic noise in magnetic disk data storage devices.
Computer systems generally include a central processor unit and a random access memory which are coupled together via a system bus. In order to store large quantities of data for use by the computer system typically a magnetic disk storage device is utilized. Magnetic disk storage devices generally include a plurality of disks which rotate at a preselected speed, and an actuator for moving a head carrier that supports transducers (read/write heads) across the rotating disks to write data to or read data from concentric data tracks on the disks. The actuator moves the transducer in a radial direction across the rotating disks in response to an input signal which controls supply of an electrical current to a motor in the actuator that governs the movement of the actuator for exerting a force to the transducer.
To access data on disk tracks, in a seek operation the transducer is moved radially across the tracks from a starting track to a destination track where the data resides. Thereafter, the rotation of the disk rotates the data on the destination track under the transducer for writing data to or reading data therefrom. The amount of time required for accessing the data, or access time, includes the time spent for the seek operation in positioning a transducer over a destination track, settling time, and a rotational latency which is the time for the data on the destination track to rotate under the transducer.
As computer processor speeds increase, there is a concomitant need to decrease access times to information stored on mass storage devices such as hard disk drives. In order to access information quickly, it is desirable for the transducer of a disk drive to be able to change its position rapidly during a seek operation. As such, in conventional disk drives, the transducer is moved between data tracks by supplying electrical currents to the actuator to initially accelerate the transducer from the starting track and then decelerate the transducer to the destination track.
However, the transition from acceleration to deceleration in conventional disk drives is generally defined by a sudden change in the polarity of the actuator current from full power in one direction (e.g. positive) to full power in an opposite direction (e.g. negative). This rapid change in current exerts rapidly changing forces on the actuator, causing vibration of the actuator and the disk drive, and resulting in acoustical noise. The acoustical noise is highly undesirable, specially in the office environment where an increasing number of disk drives are utilized. Further, the vibration of the actuator further increases the settling time.
To reduce the vibrations and acoustical noise, in some conventional disk drives a predetermined transducer radial velocity profile is stored in memory, wherein the velocity profile defines programmed actuator current levels for the seek operation. As such, the transducer is moved across the disk without radial position or velocity feedback to control the movement of the transducer.
However, using a velocity profile to control actuator currents does not take real-time transducer motion information into consideration for controlling the actuator current for minimizing vibration and acoustical noise. There is, therefore, a need for method and apparatus for reducing vibration acoustical noise induced during seek operations in disk drives, wherein the transducer motion information is utilized to control movement of the transducer.
The present invention satisfies these needs. In one embodiment, the present invention provides a method for radially moving a transducer over a storage surface of a rotating data disk including multiple concentric data tracks, for reducing noise generated during a seek operation from a starting track to a destination track on the disk. The transducer is radially moveable relative to the data tracks by an actuator in proportion to an input signal to the actuator, wherein the transducer is initially accelerated away from the starting track to a radial transition location between the starting track and the destination track, and then decelerated toward the destination track from the transition location. The method comprises the steps of: (a) detecting a radial location of the transducer in relation to the disk tracks; (b) detecting the distance between the detected transducer location and the transition location; (c) estimating a time interval for the transducer to traverse the detected distance; and (d) regulating the input signal as a function of the estimated time interval to control the rate of change of radial velocity of the transducer across the disk.
Steps (a) through (d) are performed repetitively. Step (d) can further include the steps of regulating the input signal to control variation in the rate of change of the radial velocity of the transducer. Further, the step of regulating the input signal can include the steps of limiting the magnitude of the input signal as a function of the estimated interval. Step (c) can further include the steps of: detecting the radial velocity of the transducer across the disk at the detected transducer location; detecting the rate of change of the radial velocity of the transducer at the detected transducer location; and estimating the time interval as a function of: (1) the detected distance, (2) the detected radial velocity, and (3) the detected rate of change of the radial velocity.
Preferably, the concentric data tracks are perodically interrupted by a plurality of embedded radial servo sectors per rotation, wherein each servo sector recorded with head position information and defining a sampling interval. In that case, step (a) further includes the steps of detecting the radial location of the transducer by detecting the is head position information in a servo sector passing under the transducer; and step (d) further includes the steps of: (1) estimating a number of sampling intervals in the estimated interval; (2) comparing the estimated number of sampling intervals to a preselected number; and (3) if the estimated number of sampling intervals is less than the preselected number, then regulating the input signal as a function of the estimated number of sampling intervals to control the rate of change of radial velocity of the transducer across the disk. Step (d)(3) can further include the steps of: if the estimated number of sampling intervals is greater than or equal to the preselected number, then regulating the input signal to maintain the rate of change in radial velocity of the transducer at a predetermined level.
During the acceleration of the transducer, step (b) further includes the steps of detecting the forward distance between the transducer location and the transition location as said detected distance; and step (d) further includes the steps of regulating the input signal to decrease the acceleration of the transducer toward the transition location to achieve zero transducer acceleration over the transition location. Similary, during said deceleration of the transducer, step (b) further includes the steps of detecting the backward distance between the transducer location and the transition location as said detected distance; and step (d) further includes the steps of regulating the input signal to increase the deceleration of the transducer from the transition location.
In another aspect the present invention provides a servo controller implementing the above steps for controlling seek operations in said disk drive. In one embodiment, the servo controller comprises: a location detector for detecting successive radial locations of the transducer relative to the disk tracks in response to successive clocking signals during the seek operation; and a programmed digital controller connected to said location detector, wherein the programmed digital controller is configured by program instructions for performing the following steps for each detected transducer radial location: (a) determining the distance between the detected transducer location and the transition location; (b) determining the radial velocity of the transducer across the disk at the detected transducer location; (c) determining the rate of change of the radial velocity of the transducer across the disk at the detected transducer; and (d) generating a control signal for regulating the input signal as a function of: (1) the detected distance, (2) the detected radial velocity, and (3) the detected rate of change of the radial velocity, to control the rate of change of the radial velocity of the transducer.
The data disk can include the concentric data tracks described above, wherein the location detector detects the radial location of the transducer by detecting the head position information in a servo sector passing under the transducer; and the programmed digital controller is further configured by program instructions to perform the steps of: estimating a number of sampling intervals passing the transducer over the detected distance, as a function of each detected distance, radial velocity, and rate of change of radial velocity; comparing the estimated number of sampling intervals to a preselected number; and if the estimated number of sampling intervals is less than the preselected number, then generating the control signal to regulate the input signal as a function of the estimated number of sampling intervals to control the rate of change of radial velocity of the transducer across the disk. And, the programmed digital controller can be further configured by program instructions to perform the steps of: if the estimated number of sampling intervals is greater than or equal to the preselected number, then generating the control signal to regulate the input signal to maintain the rate of change in radial velocity of the transducer at a predetermined level.
In one version, the programmed digital controller generates the control signal to regulate the input signal by limiting the magnitude of the input signal as a function of: the detected distance, (2) the detected radial velocity, and (3) the detected rate of change of the radial velocity, to control the rate of change of the radial velocity of the transducer. During the acceleration of the transducer the programmed digital controller detects the forward distance between the detected transducer radial location and the transition location as said detected distance, and generates the control signal to regulate the input signal to decrease the acceleration of the transducer toward the transition location to achieve zero transducer acceleration over the transition location. And, during the deceleration of the transducer the programmed digital controller detects the backward distance between the detected transducer radial location and the transition location as said detected distance, and generates the control signal to regulate the input signal to increase the deceleration of the transducer from the transition location.
As such, according to one embodiment of the present invention, by generating a control signal to decrease said actuator input signal for decreasing the transducer acceleration in the vicinity of the transition location to achieve zero velocity as the transducer passes over the transition location, and then by increasing said input signal in the vicinity of the transition location for increasing transducer deceleration from the transition location, rapidly changing forces to the actuator during transition from acceleration to deceleration are reduced, resulting in reduced acoustic noise and vibration.